1. Field of the Invention
This invention relates generally to a tuner and, more particularly, is directed to a tuner for a television receiver for receiving a plurality of bands, such as VHF band and UHF band.
2. Description of the Prior Art
A prior art tuner for receiving, for example, VHF and UHF bands is constructed as shown in FIG. 1.
In FIG. 1, reference numeral 1 designates a shielding case of a tuner proper. This shielding case 1 incorporates therein an electronic tuning tuner circuit section 10. Reference numeral 2 designates another shielding case which incorporates therein a PLL system channel selection circuit section 20. That is, the prior art tuner shown in FIG. 1 comprises the electronic tuning tuner circuit section 10 and the PLL system channel selection circuit section 20. The electronic tuning tuner circuit section 10 will be described first. Referring to FIG. 1, at one side surface of the shielding case 1, there is provided an input terminal 1a to receive a high frequency (RF) signal from the outside. The signal supplied to the input terminal 1a is supplied to a tuning circuit 11V formed by a diode, such as a variable capacitor (vari-cap) diode and the like for forming a VHF tuner. Also, this signal is supplied to a tuning circuit 11U formed similarly by a diode, such as a vari-cap diode and the like for forming a UHF tuner. The signal from the tuning circuit 11V is supplied through a high frequency amplifier 12V and a tuning circuit 13V to a mixer 14V in which it is mixed with the signal from a local oscillator 15V to be an intermediate frequency (IF) signal. The intermediate frequency signal from the mixer 14V is delivered to an output terminal 1b.
In like manner, the signal from the tuning circuit 11U is supplied through a high frequency amplifier 12U and a tuning circuit 13U to a mixer 14U in which it is mixed with the signal from a local oscillator 15U to be an intermediate frequency (IF) signal. The intermediate frequency signal from the mixer 14U is delivered to the output terminal 1b via the mixer 14V which, at that time, operates as an amplifier. Reference numeral 16 designates a shielding plate. Reference numeral 1c designates a power supply terminal, 1d an earth terminal, and 1e, 1f and 1g terminals to which UHF, VHF high and VHF low switching control signals are supplied and which are all aligned on one side surface of the shielding case 1. Thus, the electronic tuning tuner circuit section 10 is constructed.
Subsequently, the PLL system channel selection circuit section 20 of this tuner will be described. Referring to FIG. 1, the PLL system channel selection circuit section 20 is incorporated within the shielding case 2 as earlier noted. This PLL system channel selection circuit section 20 is formed of a channel-selection IC 21 and a crystal resonator 22 connected to the IC 21. The IC 21 is supplied with the detecting signals from the local oscillators 15V and 15U incorporated in the shielding case 1 and the tuning control signal from the IC 21 is supplied to vari-cap diodes and so on of the tuning circuits 11V, 11U, 13V and 13U incorporated in the shielding case 1. Reference numeral 2a designates a terminal through which a channel-selection control digital signal from a memory (not shown) or the like is supplied to the IC 21. Reference numerals 2b and 2c designate a power supply terminal and an earth terminal, respectively.
As described above, the reception and channel selection of the VHF band and the UHF band can be carried out. In this prior art tuner, a signal line 2d through which the tuning control voltage is supplied may be formed of a standard or normal wire because the signal passed therethrough is a DC signal. On the other hand, a signal line 2e through which the detecting signals from the local oscillators 15V and 15U are supplied to the IC 21 must be formed of a shielding wire because the signal is the high frequency signal. This increases the number of processes in the assembly process of the tuner to a television receiver set and is very disadvantageous in a manufacturing standpoint.
FIG. 2A is a circuit block diagram showing another example of the prior art tuner. In FIG. 2A, like parts corresponding to those of FIG. 1 are marked with the same references and will not be described in detail. In the prior art tuner shown in FIG. 2A, the shielding case 2 is close to and fixed to the shielding case 1 by soldering and so on to thereby remove the signal line 2e, which has to be shielded. Accordingly, if the above mentioned tuner is manufactured in advance, the assembly process for assembling the tuner into a television receiver set or the like can be made easy. In this case, however, the terminals 1c to 1g and the terminals 2a to 2c are provided on the different planes of the tuner so that in the assembly process of the tuner to the television receiver set, the connection work to the external terminals becomes complicated.
Therefore, it is proposed to align the positions of the terminals 1c to 1g and 2a to 2c in line by making the shape of the shielding case 2 same as that of the shielding case 1 as shown in FIG. 2B. According to this method, however, as will be clear from FIG. 2B, the space factor of the tuner grows worse extremely.